It is self evident that all measured motions require a reference. Although, according to Einstein (1905), there is no preferred reference frame, that is, no propagation medium or “ether” required for comparing (measuring) motion of objects or electromagnetic waves (light). Einstein claimed that only relative motion between systems was important, not motion relative to a propagation medium, without specifying any alternative transmission mechanism in place of the medium (inferring that light does not require a propagation medium). This claim is in direct conflict with the basic electromagnetic (EM) wave theory developed by Maxwell (1865) who established EM wave propagation, predicting the transmission of light based on a since-measured propagation medium. Further, an ether-less Universe is not supported by Lorentz's (1899) motional transform, which is also shown to be based on Maxwell's propagation medium. Techniques concerning measuring motion in space relative to such a medium, however, have been discouraged or believed not possible. Logically (according to these beliefs), if there is no propagation medium, and space is empty, then it should be impossible to measure motion in space.
The Michelson and Morley Experiment (MMX) (1887) designed to measure the Earth's motion with respect to the propagation medium, was an insensitive method of measuring motion. Even if there were relative motion with respect to the medium, at Earth orbital speeds of 30 km/s (or Mach number M=v/c=10−4, where v is the system velocity and c is the speed of light), only a small fraction of an interference fringe (2π radians) would have been measured, and at Earth's rotation speed of 480 m/s (M≈1.5×10−6) nothing would have been detected. Because the MMX failed to detect the relative motion of the Earth through any propagation medium, this negative result was interpreted as evidence against the existence of a propagation medium. Even if the system had been sensitive enough to detect relative motion, no motion would have been detected, as shown below, because the propagation medium moves with the Earth.
To establish motion with respect to the medium at practical speeds on Earth, as well as at higher speeds in outer space, a more sensitive measurement system would have been required. The MMX was insensitive because it was based on a second order velocity term (M2) as explained below. The MMX relied on the difference in the propagation times in each direction in a round trip propagation measurement, where the propagation differences in each direction tended to cancel one another. One of the main reasons why the propagation medium is not readily detectable is that there is no existing dedicated measurement system sensitive enough to detect linear motion relative to the medium.
It is shown that Sagnac (1913) demonstrated rotary motion relative to the propagation medium. Sagnac split a beam of light into two beams traveling in opposite directions using a beam splitter. The beam splitter is used to measure the propagation delay in and against the direction of rotating mirrors, relative to the propagation medium. Sagnac reflected light, around a loop relative to the Earth's surface, using a rotating square of four mirrors. FIG. 1 shows Sagnac's mirror system 10 including a rotating frame 20a and 20b, mirrors 31-34 (mirror 31 being a half-silvered mirror), a radius 42, a side length l 44, and an angular velocity 46. A light source 50 projects a beam of light which is split by mirror 31; both beams travel in opposite directions and end at a detector 55. One light beam propagates in the medium against the mirror motion, counter-clockwise. The other light beam propagates in the medium with the direction of mirror motion, clockwise, through the half-silvered mirror. The mirror system 10 must have caused the shift in interference fringes as a consequence of the different distances that light traveled in the propagation medium (stationary on the Earth's surface) due to the rotation of the mirror system relative to the propagation medium. If there had been no medium, or if the medium rotated with the mirrors, there would have been no effect, no relative motion, and no Propagation Time Asymmetry (PTA).
In system 10, light passes around the mirrors having a peripheral distance d (d=41) in a propagation time t=±d/c (depending on the light direction), where c is the speed of light at the Earth's surface. If the mirror system rotates with an angular velocity v then the incremental distance traveled in time t (by the spinning mirrors) is Δd=vt=±vd/c. The incremental prediction equation for the propagation time asymmetry (PTA) is shown below in Equation (1).Δt=Δd/c=vd/c2=Mt, where M=v/c<<1  (1)
The incremental time Δt between the light beams was measured through interference fringe movement in an interferometer at the detector. By measuring Δt and knowing d and c, the angular velocity of the spinning mirrors at the Earth's surface can be calculated exactly according to Equation (1) and Maxwell's EM wave theory, providing the medium is at rest on the Earth's surface. Although Sagnac demonstrated that his result confirmed the existence of Maxwell's stationary propagation medium, others maintained that the Sagnac effect was consistent with special relativity and that the medium did not exist. This is not possible; unless Maxwell's wave theory, based on a propagation medium, is shown to be in error, which is not the case, as it has been reliably used for over 150 years. Also, any relativistic effects at these mirror speeds are negligible compared to Sagnac's classical PTA effect.
Recent patents for measuring motion in space are, for example, those of Wang et al. (U.S. Pat. Nos. 6,813,006 and 7,586,587). In the first patent they proposed to measure motion by measuring the time difference of light passing through two different media. In the second they proposed to measure motion using two beams of interfering light. The resulting interference pattern (standing wave) is used to calculate the system speed. But these patents do not identify any mechanism by which the propagation occurs, i.e., whether it is relative to the Earth's surface, to a vacuum medium or to some other unknown process. A non-preferred reference is not an option in electromagnetic theory; it is not a solution of Maxwell's EM wave equation, it is non-causal (non predictable). If the Earth's surface is assumed to be the reference then the motion will be defined relative to the propagation medium stationary on the Earth's surface. Therefore, it is recognized that improved and consistent techniques for measuring speed in outer space as well as on Earth are desirable.